Lacquer and ink are formed by adding coloring agents and other additives in response to their uses to solvents by the medium of binder resins. Polyvinyl acetal resins are used as a binder resin in the field of lacquer and ink because of high characteristics in a film formation property, dispersibility of a pigment, adhesion property to a surface to be coated and alcohol-solubility.
A polyvinyl acetal resin is normally prepared by using an acid catalyst to polyvinyl alcohol and reacting it with an aldehyde. But, when the polyvinyl acetal resin is prepared by this method, there were problems that since the aldehyde remains in the polyvinyl acetal resin, the polyvinyl acetal resin was colored due to the occurrence of oxides of the aldehyde and reactants of aldehydes with each other and therefore color of a lacquer and ink composition to be formed was changed, and a foul odor was generated, and the viscosity of the lacquer and ink composition was increased during being stored for long periods. In Japanese Kokai Publication Hei-11-349889, there is disclosed printing ink and lacquer containing polyvinyl butyral resin which uses polyvinyl acetal partially hydrolyzed as a raw material, but there is no description of a foul odor or storage stability for long periods.
Further, when a polyvinyl acetal resin is prepared by acetalization of polyvinyl alcohol, an antioxidant is normally added to a reaction system or into resin for the protection of the aldehyde against oxidation and for the protection against oxidation and an improvement in heat resistance of the polyvinyl acetal resin to be formed. However, since the antioxidant reduces the dispersibility of a pigment of a lacquer and ink composition to be obtained and further has a problem in a safety point when it is used as ink material for the packaging of foods and pharmaceutical products, an amount of the antioxidant used needed to be restricted to the utmost.